Image forming apparatus

Abstract

An image forming apparatus includes an image bearing member, a first conductive member, a bias application device, and a control portion, and performs image formation on a surface of the image bearing member while making the image bearing member rotate. The image forming apparatus is capable of executing a heating-up mode in which, at the time of non-image formation, in a state where the image bearing member is made to rotate at a velocity lower than that used at the time of image formation, an alternating current bias having a frequency higher than that used at the time of image formation and a peak-to-peak value twice or more as large as a discharge start voltage between the first conductive member and the image bearing member is applied to the first conductive member to cause a surface of the image bearing member to be heated up.

What is claimed is: 
     
       1. An image forming apparatus, comprising:
 an image bearing member that has a photosensitive layer formed on an outer peripheral surface thereof; 
 a first conductive member that makes contact with the photosensitive layer of the image bearing member; 
 a bias application device that applies a bias including an alternating current bias to the first conductive member; and 
 a control portion that controls the bias application device, 
 wherein 
 image formation is performed on a surface of the image bearing member while the image bearing member is made to rotate, and 
 the image forming apparatus is capable of executing a heating-up mode in which, at a time of non-image formation, in a state where the image bearing member is made to rotate at a velocity lower than that used at a time of image formation, an alternating current bias having a frequency higher than that used at the time of image formation and a peak-to-peak value twice or more as large as a discharge start voltage between the first conductive member and the image bearing member is applied to the first conductive member to cause a surface of the image bearing member to be heated up. 
 
     
     
       2. The image forming apparatus according to  claim 1 , wherein
 a temperature and humidity detection device that detects a temperature and a humidity inside the image forming apparatus is provided, and 
 the control portion changes, in accordance with a temperature and a humidity that are detected by the temperature and humidity detection device, a frequency of an alternating current bias to be applied to the first conductive member at a time of executing the heating-up mode. 
 
     
     
       3. The image forming apparatus according to  claim 1 , wherein
 in accordance with an energization time that is a duration of energizing the image bearing member since a start of use of the image bearing member, the control portion increases, in stages, a frequency of an alternating current bias to be applied to the first conductive member at a time of executing the heating-up mode. 
 
     
     
       4. The image forming apparatus according to  claim 1 , wherein
 at a time of executing the heating-up mode, an alternating current bias having a frequency in such a range that no discharge occurs between the image bearing member and the first conductive member is applied. 
 
     
     
       5. The image forming apparatus according to  claim 1 , wherein
 the bias application device is capable of applying, to the first conductive member, a bias obtained by superimposing an alternating current bias on a direct current bias, and 
 at a time of executing the heating-up mode, a bias obtained by superimposing a direct current bias not higher than the discharge start voltage between the first conductive member and the image bearing member on the alternating current bias is applied. 
 
     
     
       6. The image forming apparatus according to  claim 5 , wherein
 at the time of executing the heating-up mode, a direct current bias to be applied to the first conductive member is set to 0. 
 
     
     
       7. The image forming apparatus according to  claim 1 , wherein
 the first conductive member is a conductive roller obtained by forming a roller body made of a conductive material having a dielectric property on an outer peripheral surface of a metallic shaft. 
 
     
     
       8. The image forming apparatus according to  claim 1 , wherein
 the image bearing member is contacted further by at least one second conductive member, and 
 the control portion executes the heating-up mode by applying an alternating current bias to the first conductive member and the second conductive member. 
 
     
     
       9. The image forming apparatus according to  claim 8 , wherein
 to the second conductive member of some type, no bias is applied at the time of image formation. 
 
     
     
       10. The image forming apparatus according to  claim 1 , wherein
 the photosensitive layer formed on the outer peripheral surface of the image bearing member is an amorphous silicon photosensitive layer. 
 
     
     
       11. An image forming apparatus, comprising:
 an image bearing member that has a photosensitive layer formed on an outer peripheral surface thereof; 
 a first conductive member that makes contact with the photosensitive layer of the image bearing member; 
 a bias application device that applies a bias including an alternating current bias to the first conductive member; and 
 a control portion that controls the bias application device, 
 wherein 
 image formation is performed on a surface of the image bearing member while the image bearing member is made to rotate, and 
 the image forming apparatus is capable of executing a heating-up mode in which, at a time of non-image formation, in a state where the image bearing member is stopped from rotating, an alternating current bias having a peak-to-peak value twice or more as large as a discharge start voltage between the first conductive member and the image bearing member is applied to the first conductive member to cause a surface of the image bearing member to be heated up. 
 
     
     
       12. The image forming apparatus according to  claim 11 , wherein
 at a time of executing the heating-up mode, an alternating current bias having a frequency higher than that used at a time of image formation is applied to the first conductive member.